Transcript What Causes A Tornado?

Tornados
Presented by:
Bridget Bower
Sarah Weaver
Kris Brownlee
Allie Bogenschutz
What Causes A Tornado?
1. Warm air moves north. It collides
with cold winds and dry breezes.
2. The moisture in the warm air
rises and condenses into large
clouds.
3. The clouds grow larger and larger.
Finally, a thunderstorm is brewed up
with a strong updraft.
4. The air starts to rotate.
5. The most violent tornadoes come
from a super-cell thunderstorm. A
super-cell thunderstorm is a massive
cloud structure that has fantastic
lightning and a long- lasting, strong
updraft.
6. The updraft spins upwards and feeds
energy into the super-cell. Within the
spinning winds, a spiraling column
of air is formed. This is called a
vortex. However, the tornado is not
yet formed.
7. Dry winds from the west swarm in
and up into the super-cell clouds. It
evaporates the moisture.
8. The evaporation results with the air
cooling and sinking. It acts together
with the updraft and makes the
vortex spin faster and tighter.
9. The vortex stretches downwards and
finally touches ground. This is now
our tornado!
What Damage Can It Do?
 Chimneys break.
 Roofs are torn open.
 Buildings are
crushed.
 Miscellaneous items
are blown away.
 Fields are covered
with debris.
 People could be
killed.
How Can We Stop This?
 Support buildings to keep them from being blown away or
toppled.
 There is no way of stopping a tornado, but you can always
prepare yourself.
 Keep a First Aid kit at handy.
 When it hits, find a safe place to hide it out. That would be in a
basement or closet. If either cannot be accessed, hide under a sturdy
piece of furniture.
Why Do People Still Live There?
Risk perception. (people think: “It won’t
happen to me!”)
Job
Family and friends. Home.
Too expensive to move.
Good land (tornado alley has lots of
land that is good for growing cereals)
How Can We Predict This?
Sadly, there is no way we can
accurately predict tornadoes.
But, we still can use weather balloons
to measure the weather and many
warning systems that can spread news
of on coming tornadoes quickly.
Where Do They Occur?
 Whenever and wherever conditions are right, tornados are possible, but
they are most common in the central plains of North America, east of the
Rocky Mountains and west of the Appalachian Mountains. They occur
mostly during the spring and summer; the tornado season comes early in
the south and later in the north because spring comes later in the year as
one moves northward. They usually occur during the late afternoon and
early evening. However, they have been known to occur in every state in
the United States, on any day of the year, and at any hour. They also occur
in many other parts of the world, including Australia, Europe, Africa, Asia,
and South America.
How tornadoes form?
• Prior to a thunderstorm, a
change in the direction of wind,
and increase in wind speed
with increase in height. An
invisible, horizontal spinning
affect is created in the lower
atmosphere.
BB
• Next, rising air forces the
updraft to tilt the rotating air from
horizontal to vertical.
BB
• An air area extends 2-6
miles throughout the storm
BB
• A rotating wall is then formed.
• The rotating wall is formed
when the storm intensifies the
updraft in low-level air from
several miles away. Some of
this low-level air Is pulled into
the updraft from the rain area.
This rain-cooled air is humid
and the moisture condenses to
form a wall-cloud.
BB
• Lastly, a tornado is formed.
BB
What are the conditions needed for
a tornado to form?
• Moisture in the lower to middle of the
atmosphere
• Unstable air, that will continue to rise.
• In some cases a lifting force needs to be
present to help the air to begin to rise.
BB
The Fujita Scale of Tornado Intensity
•The Fujita Scale is used to rate the intensity of a
tornado by examining the damage caused by the
tornado after it has passed over a man-made
structure.
•Professor Fujita and Allen Pearson, directors of
the NSSFC (National Severe Storm Forecast
Center) in 1971 both created the scale, also known
as The Fujita – Pearson Scale.
•There are 6 parts to the scale.
•SW
Category F0: Light Damage (<73 mph); Some damage to
chimneys; branches broken off trees; shallow-rooted trees
pushed over;
sign boards damaged.
Category F1: Moderate Damage (73-112 mph); Peels
surface off roofs;
mobile homes pushed off foundations or
overturned; moving autos blown off road.
Category F2: Considerable Damage (113-157 mph); Roofs
torn off
frame houses; mobile homes demolished;
boxcars overturned;
large trees snapped or uprooted;
light-object missiles generated; cars lifted off ground.
Category F3: Severe Damage (158- 206 mph); Roofs and
some walls torn off well-constructed houses, trains
overturned; most trees in forest uprooted; heavy cars lifted
off ground and thrown.
SW
Category F4: Devastating Damage (207- 260 mph); Well-constructed
houses leveled; structure with weak foundations blown off
some distance; cars thrown and large missiles generated.
Category F5: Incredible Damage (261- 318 mph); Strong frame
houses lifted off foundations and swept away; automobile sized
missiles fly through the air in excess of 100 meters (109 yards);
trees debarked; incredible phenomena will occur.
Category F6: Inconceivable Tornado (319 – 379 mph); These winds
are very unlikely. The small area of damage they might
produce would probably not be recognizable along with the
mess produced by F4 and F5 wind that would surround the F6
winds. Missiles, such as cars and refrigerators would do
serious secondary damage that could not be directly identified
as F6 damage. If this level is ever achieved, evidence for it
might only be found in some manner of ground swirl pattern, for
it may never be identifiable through engineering studies. SW
• Tornadoes Occur Anywhere
• Carolinas Outbreak:
• March 28, 1984, afternoon-evening
22 tornadoes
57 deaths
1,248 injuries
damage $200 million
37% of fatalities in mobile homes
• Pennsylvania-Ohio Outbreak:
• May 31, 1985, late afternoon-evening
41 tornadoes, including 27 in PA and OH
75 deaths in US
1,025 injuries
damage $450 million
• Plains Outbreak:
• April 26-27, 1991, afternoon of 26th through early morning 27th
54 tornadoes
21 deaths
308 injuries
damage $277+ million
15 deaths in/near mobile homes, 2 deaths in vehicles. SW
Frequency of Tornadoes
Tornadoes can occur at any time of the year.
In the southern states, peak tornado occurrence is in March through
May, while peak months in the northern states are during the
summer.
Note, in some states, a secondary tornado maximum occurs in the
fall.
Tornadoes are most likely to occur between 3 and 9 p.m. but have
been known to occur at all hours of the day or night.
The average tornado moves from southwest to northeast, but
tornadoes have been known to move in any direction. The average
forward speed is 30 mph but may vary from nearly stationary to 70
mph.
The total number of tornadoes is probably higher than indicated in
the western states. Sparse population reduces the number reported.
SW
Office Buildings: go to an interior hallway on
the lowest floor
Homes: go to the basement or a place in the
middle of the house, like a closet, bathroom, etc.
Shopping Centers: Do NOT go to your car! If
there isn't a pre-designated shelter, go to a middle
hallway on the lowest floor.
Schools: Stay away from auditoriums or
gymnasiums with wide, huge roofs that could
collapse easily
Cars/Mobile Homes: leave them and find
shelter in a building. If there is no shelter nearby,
move away from the tornado's path. Lie flat in
the nearest ditch, ravine or culvert with your
hands shielding your head.
-Defense Supply Center, Columbus
“…more deaths occured in a single city than from any
other tornado in U.S. history.” –tornadoproject.com
Towns: Murphysboro, Gorham, DeSoto
Date: March 18, 1925 Deaths: 695 Injured: 2027
Tornadoes can occur in any month but March through June is
considered tornado season. Historically, the most destructive
tornadoes strike in March and April.
2nd Most Destructive: The
Natchez Tornado
Towns: Concordia, LA & Adams,
MS
Date: May 7, 1840
Deaths: 317 Injured: 109
3rd Most Destructive: St.
Louis Tornado of 1896
Towns: St. Louis, MO &Madison,
IL
Date: May 27, 1896
Deaths: 255 Injured: 1000
4th Most Destructive: The Tupelo
Tornado
Towns: LEE / ITAWAMBA
Date: April 6, 1936
Deaths: 216 Injured: 700
5th Most Destructive: The Gainesville
Tornado
Towns: HALL
Date: April 6, 1936
Deaths: 203 Injured: 1600
In the early morning hours of April 9, 1999, tornadoes swept through
Cincinnati, killing four and causing more than $25 million in damage to
homes and businesses.
• April 9, 1999
• Sycamore/Symmes Township
• Four Dead
Sources
http://federalvoice.dscc.dla.mil/federalvoice/020313/Tornado.html
http://www.tornadoproject.com/toptens/toptens.htm#top
http://www.cincinnati.com/tornado/
http://www.noaa.gov/tornados.html
http://whyfiles.news.wisc.edu/013tornado/predict.html
http://www.fema.gov/library/tornadof.htm
http://www.indystar.com/library/factfiles/history/weather/tornadoes.html
Sands, Stella. Kids Discover Tornadoes. New York: Kids Discover 1996